Recovery Of Helium From Nitrogen-Rich Streams

ABSTRACT

Overall power consumption in a cryogenic distillation process for recovering helium from nitrogen-rich gases comprising helium may be reduced if the feed to the distillation column system is at least substantially condensed by indirect heat exchange against a first bottoms liquid at first pressure, and a second bottoms liquid at a second pressure that is different from the first pressure.

BACKGROUND OF THE INVENTION

This invention relates to the recovery of helium from nitrogen-rich gas.The invention has particular application in the recovery of helium fromnitrogen-rich natural gas from an underground source.

U.S. Pat. No. 5,167,125A discloses a process for recovering light gasessuch as hydrogen, neon and helium, from gas stream containing higherboiling components such as nitrogen and C₁₋₂ hydrocarbons. According tothe embodiment depicted in FIG. 1 of U.S. Pat. No. 5,167,125A, a stream100 of feed gas is cooled by indirect heat exchange and the cooled feedgas 110 is reduced in pressure across valve 112 and fed to adistillation column 102 where it is separated into bottoms liquiddepleted in light gas(es), and overhead vapor enriched in light gas(es).The bottoms liquid is reboiled using the feed gas in reboiler 108 toprovide vapor for the column. Nitrogen in the overhead vapor iscondensed in the overhead condenser 116 by indirect heat exchangeagainst a stream 104 of bottoms liquid that is expanded across valve122, and the resultant liquid nitrogen is recycled to the column asreflux 120. A stream 118 of impure helium gas is removed from condenser16.

BRIEF SUMMARY OF THE INVENTION

It is an objective of the present invention to provide an improvedprocess for recovering helium from nitrogen-rich gases comprisinghelium, particularly nitrogen-rich natural gas from underground sources.

It is an objective of preferred embodiments of the present invention toreduce the overall power required to recover helium from such gases.Helium may be recovered at a higher pressure than in prior proceses andwith reduced loss.

It is also an objective of preferred embodiments of the presentinvention to reduce the capital and operating costs of apparatus forrecovering helium from such gases.

According to a first aspect of the present invention, there is provideda process for recovering helium from a nitrogen-rich feed gas comprisinghelium. The process comprises cooling a pressurized nitrogen-rich feedgas comprising helium to produce cooled feed; and separating said feedin a first distillation column system operating at an elevated operatingpressure to produce helium-enriched overhead vapor and nitrogen-enrichedbottoms liquid. The process is characterized in that the feed to thefirst distillation column system is at least partially condensed; andthat the cooling of the feed gas is achieved by indirect heat exchangeagainst at least a first bottoms liquid at a first elevated pressure anda second bottoms liquid at a second elevated pressure that is differentfrom the first elevated pressure.

According to a second aspect of the present invention, there is providedapparatus for recovering helium from a nitrogen-rich feed gas comprisinghelium, said apparatus comprising:

a distillation column system for operation at an elevated operatingpressure to separate at least partially condensed feed gas intohelium-enriched overhead vapor and nitrogen-enriched bottoms liquid;

-   -   an overhead condenser for partially condensing helium-enriched        overhead vapor by indirect heat exchange to produce        helium-enriched vapor as product and liquid for reflux in the        column system;    -   a first heat exchange system for cooling feed gas by indirect        heat exchange with a first nitrogen-enriched bottoms liquid to        produce cooled feed gas and vapor for the column system;    -   a first pressure reduction device for reducing the pressure of a        second nitrogen-enriched bottoms liquid to produce reduced        pressure bottoms liquid;    -   a second heat exchange system for cooling said cooled feed gas        by indirect heat exchange against said reduced pressure bottoms        liquid to produce at least partially condensed feed gas and at        least partially vaporized bottoms liquid; and    -   a second pressure reduction device for reducing the pressure of        said at least partially condensed feed gas to produce at least        partially condensed feed gas at reduced pressure for use as said        feed to the distillation column system.

According to an alternative arrangement of the second aspect of thepresent invention, there is provided apparatus for recovering heliumfrom a nitrogen-rich feed gas comprising helium, said apparatuscomprising:

-   -   a distillation column system for operation at an elevated        operating pressure to separate at least partially condensed feed        gas into helium-enriched overhead vapor and nitrogen-enriched        bottoms liquid;    -   an overhead condenser for partially condensing helium-enriched        overhead vapor by indirect heat exchange to produce        helium-enriched vapor as product and liquid for reflux in the        column system;    -   a first pump for pumping a second nitrogen-enriched bottoms        liquid to produce pumped bottoms liquid;    -   a first heat exchange system for cooling feed gas by indirect        heat exchange with said pumped bottoms liquid to produce cooled        feed gas and nitrogen-enriched vapor;    -   a second heat exchange system for cooling said cooled feed gas        by indirect heat exchange against a first nitrogen-enriched        bottoms liquid to produce at least partially condensed feed gas        and vapor for the column system; and    -   a pressure reduction device for reducing the pressure of said at        least partially condensed feed gas to produce at least partially        condensed feed gas at reduced pressure for use as said feed to        the distillation column system.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a flowsheet depicting a comparative process for recoveringhelium from nitrogen-rich natural gas in which the feed to the columnsystem is predominantly gaseous (see Comparative Example 1);

FIG. 2 is a flowsheet depicting a helium recovery process according tothe present invention in which the feed to the column is predominantlyliquid (see Example 1);

FIG. 3 is a flowsheet depicting a modified process of FIG. 2 in which afurther portion of the bottoms liquid is expanded to an intermediatepressure and used to provide refrigeration duty in the separation (seeExample 2);

FIG. 4 is a flowsheet depicting a modified process of FIG. 3 where thefeed is at higher pressure and part of the helium-free product is pumpedand used to cool the feed upstream of the column reboiler (see Example3);

FIG. 5 is a flowsheet depicting a preferred process in which most of thenitrogen product is expanded to provide refrigeration to provide somehelium-free liquid nitrogen as product (see Example 4);

FIG. 6 is a flowsheet depicting a modified process of FIG. 5 in whichliquid product is subcooled in the column overhead condenser beforebeing reduced in pressure to the storage tank (see Example 5);

FIG. 7 is a flowsheet depicting a process according to the presentinvention in which the helium recovery process is integrated with anupstream an NGL recovery column (see Example 6);

FIG. 8 is a flowsheet depicting the helium recovery process integratedwith a downstream nitrogen purification column system (see Example 7);and

FIG. 9 is a flowsheet depicting a fully integrated scheme for processingnitrogen-rich natural gas from an underground source involving NGLrecovery, HP and LP columns for nitrogen production, liquid nitrogenproduction and helium purification by PSA (see Example 8).

DETAILED DESCRIPTION OF THE INVENTION

All references herein to pressure are references to absolute pressureand not gauge pressure unless expressly stated otherwise. In addition,references to the singular should be interpreted as including the pluraland vice versa, unless it is clear from the context that only thesingular or plural is meant. Further, unless expressly stated otherwise,fluid compositions are calculated in mol. % on a “dry” basis, i.e.excluding any water content from the calculations. In reality, to avoidoperating problems, water content must be low enough, typically no morethan 10 ppm, to avoid freeze-out and/or hydrate formation at the coldend of the process.

The terms “elevated pressure” and “pressurized” are intended to mean apressure that significantly more than atmospheric pressure. The termsare intended to exclude insignificant increases in pressure, e.g.produced by a fan, simply to overcome pressure drop in apparatus that isoperating at about atmospheric pressure. By use of the terms “elevatedpressure” and “pressurized”, the Inventors are typically referring toabsolute pressures of at least 1.5 bar, e.g. at least 2 bar.

The term “indirect heat exchange” means that sensible and/or latent heatas appropriate is transferred between fluids without the fluids inquestion coming into direct contact with each other. In other words,heat is transferred through a wall of a heat exchanger. The term isintended to include the use of an intermediate heat transfer fluid whereappropriate.

The term “distillation” is intended to include rectification andfractionation.

Overview of the Process

The process involves cooling a pressurized nitrogen-rich feed gascomprising helium to produce cooled feed; and separating the feed in afirst distillation column system operating at an elevated operatingpressure to produce helium-enriched overhead vapor and nitrogen-enrichedbottoms liquid. The feed to the first distillation column system is atleast partially condensed. The cooling of the feed gas is achieved byindirect heat exchange against at least a first nitrogen-enrichedbottoms liquid at a first elevated pressure and a secondnitrogen-enriched bottoms liquid at a second elevated pressure that isdifferent from the first elevated pressure.

The first and second nitrogen-enriched bottoms liquids are typicallytaken from the sump of the first distillation column system and may bedifferent portions of the same bottoms liquid. However, one of thebottoms liquids could be taken from a different point at the bottom ofthe distillation column system.

The compositions of the first and second nitrogen-enriched bottomsliquids are usually at least substantially identical although slightvariations may be observed depending on the precise location in the sumpof the distillation column system at which the bottoms liquid is used tocool the feed, or from which the bottoms liquid is extracted for use incooling the feed. However, any variations in composition that may bepresent would be too small to have any significant effect on theoperation of the process.

Cooling and Condensing the Feed

The first elevated pressure is typically equal to the elevated operatingpressure of the first distillation column system. In this regard, thefirst elevated pressure is usually from about 2 bar to about 35 bar, andpreferably from about 10 bar to about 30 bar.

The second elevated pressure may be more than or less than the elevatedoperating pressure of the first distillation column system. Thedifference between the first and second elevated pressures is typicallyat least 1 bar, e.g. at least 2 bar, for example at least 5 bar or, insome embodiments, at least 10 bar.

Typically, the vaporization pressure of the second nitrogen-enrichedbottoms liquid is relatively close to the feed pressure (either pumpedor expanded) whether it is taken as pressurized product or it getsexpanded.

In embodiments in which the second elevated pressure is less than theelevated operating pressure of the first distillation column system, thesecond elevated pressure is typically significantly more than 1 bar, e.gat least 1.5 bar or from 2 bar to about 30 bar, and preferably from 5bar to 25 bar. In such embodiments, bottoms liquid is expanded toproduce the second bottoms liquid.

In embodiments in which the second elevated pressure is greater than theelevated operating pressure of the first distillation column system, thesecond elevated pressure may be from about 3 bar to about 150 bar, andpreferably from about 10 bar to 100 bar. In such embodiments, bottomsliquid is pumped to produce the second the bottoms liquid.

The feed gas may be at subcritical pressure or supercritical pressure.

In embodiments in which the feed gas is at subcritical pressure, thefeed gas may cooled (and possibly partially condensed) by indirect heatexchange against the first bottoms liquid and then at least partiallycondensed (or a further portion condensed) by indirect heat exchangeagainst the second bottoms liquid.

In embodiments in which the feed gas is at supercritical pressure, thefeed gas may be cooled by indirect heat exchange against the firstbottoms liquid and then further cooled by indirect heat exchange againstthe second bottoms liquid. The pressure of the cooled feed is let downprior to being fed to the first distillation column system.

The feed to the first distillation column system typically has a vaporfraction of no more than 0.5, e.g. no more than 0.3 or no more than 0.2or even no more than 0.05. In some preferred embodiments, the feed tothe first distillation column system is at least substantially fullycondensed.

The pressurized nitrogen-rich feed gas is usually at a pressure greaterthan the elevated operating pressure of said first distillation columnsystem. In this regard, the pressurized feed is typically taken from anatural underground source. Where the pressurized feed is at a pressuregreater than the elevated operating pressure of the first distillationcolumn system, the process comprises expanding the at least partiallycondensed feed prior to separation.

The pressure of the pressurized nitrogen-rich feed gas may be from about2 bar to about 200 bar, and is typically from about 10 bar to about 100bar.

The elevated operating pressure of the distillation column system isusually from about 2 bar to about 35 bar, and preferably from about 10bar to 30 bar.

Additional Refrigeration Requirement

Throughout this specification, the term “expanding” is intended toinclude expanding to produce work (“work expansion”) and expandingisenthalpically, typically across a Joule-Thomson (or “J-T”) valve.Gases are typically work expanded in an expander whereas liquids areusually expanded isenthalpically across a valve.

The process may comprise expanding vaporized bottoms liquid, or a fluidderived therefrom, to produce expanded nitrogen-enriched gas and usingthe expanded gas to provide a part of the refrigeration duty of theprocess. The vaporized bottoms liquid is usually work expanded in anexpander.

The second nitrogen-enriched bottoms liquid is usually at leastpartially vaporized as a result of the indirect heat exchange againstthe feed gas. In such embodiments, the process may comprise warming thevaporized bottoms liquid by indirect heat exchange to produce warmednitrogen-enriched gas; expanding the warmed nitrogen-enriched gas toproduce expanded nitrogen-enriched gas; and cooling the feed gas byindirect heat exchange with the expanded nitrogen-enriched gas toproduce cooled feed gas. The warmed nitrogen-enriched gas is usuallywork expanded in an expander.

In some embodiments, the process comprises expanding a thirdnitrogen-enriched bottoms liquid to produce expanded nitrogen-enrichedfluid; vaporizing the expanded nitrogen-enriched fluid by indirect heatexchange against condensing nitrogen in the first distillation columnsystem to produce nitrogen-enriched gas; expanding the nitrogen-enrichedgas to produce expanded nitrogen-enriched gas; and condensing nitrogengas in the first distillation column system by indirect heat exchangeagainst the expanded nitrogen-enriched gas to produce liquid reflux forthe first distillation column system. The nitrogen-enriched gas istypically work expanded in an expander.

The pressure at which the expanded third bottoms liquid is vaporized istypically less than the pressure at which the expanded second bottomsliquid is vaporized.

The process may comprise expanding a fourth nitrogen-enriched bottomsliquid to produce further expanded nitrogen-enriched fluid; andvaporizing the further expanded nitrogen-enriched fluid by indirect heatexchange against condensing nitrogen in the first distillation columnsystem to produce further nitrogen-enriched gas.

The pressure at which the expanded fourth bottoms liquid is vaporized istypically less than the pressure at which the expanded third bottomsliquid is vaporized.

Where the second bottoms liquid is vaporized as a result of the indirectheat exchange against the feed gas, the process may comprise expandingthe vaporized bottoms liquid to produce expanded nitrogen-enriched gas;and condensing nitrogen gas in the first distillation column system byindirect heat exchange with the expanded nitrogen-enriched gas toproduce liquid reflux for the first distillation column system andwarmed nitrogen-enriched gas.

In such embodiments, the process may comprise expanding a third bottomsliquid to produce further expanded nitrogen-enriched fluid; andvaporizing the further expanded nitrogen-enriched fluid by indirect heatexchange against condensing nitrogen in the first distillation columnsystem to produce further nitrogen-enriched gas. The vaporizationpressure of the further expanded nitrogen-enriched fluid will typicallybe less than the vaporization pressure of the second bottoms liquid.

A fourth bottoms liquid may be expanded to form an expanded fluid whichis then separated into a vapor phase and a liquid phase. The vapor phasemay be warmed by indirect heat exchange to produce a gaseous nitrogenproduct.

Flash vapor may be formed on expanding bottoms liquid to form expandedbottoms liquid. Alternatively, the bottoms liquid could be subcooledprior to expansion and thereby avoid the formation of flash vapor. Suchsubcooling could be effected by indirect heat exchange against expandednitrogen-enriched gas.

The bottoms liquid evaporated in the overhead condenser and not expandedin an expander is typically at the lowest pressure (e.g. from about 1bar to about 10 bar) as it needs to boil at low temperature to condenseas much nitrogen as possible from the helium.

The bottoms liquid evaporated in the overhead condenser and expanded inan expander is at an intermediate pressure (e.g. from about 2 bar toabout 25 bar), and is typically only there if the vapour from the secondbottoms liquid is taken as product and not expanded (e.g see FIG. 3), sothere is no other source of expander refrigeration. This stream can beevaporated at an intermediate pressure and higher temperature tooptimise the cooling in the condenser over the whole temperaturerange—most of the condensing duty is needed at the higher temperaturewhere the nitrogen concentration in the helium is highest.

The third and fourth nitrogen-enriched bottoms liquids are typicallytaken from the sump of the first distillation column system and may bedifferent portions of the same bottoms liquid. However, one or more ofthe bottoms liquids could be taken from a different point at the bottomof the distillation column system. In some embodiments, the first,second, third and fourth bottoms liquids are different portions of thesame bottoms liquid.

The process is preferably autorefrigerated. The term “autorefrigerated”is intended to mean that all of the refrigeration duty required by theprocess is provided internally, i.e. by indirect heat exchange againstfluid streams within the process. In other words, no additionalrefrigeration is provided from an outside source.

Origin of the Feed

The feed gas may be taken from a natural gas liquid (NGL) recoverycolumn. Thus, the process may comprise cooling and at least partiallycondensing pressurized dry, carbon dioxide-free natural gas to produceat least partially condensed natural gas; and separating the at leastpartially condensed natural gas in a second distillation column systemoperating at an elevated operating pressure to produce C₂₊-depletedoverhead vapor and C₂₊-enriched bottoms liquid. In such embodiments, theC₂₊-depleted overhead vapor is the nitrogen-rich feed gas.

The process may be integrated with a process for recovering helium andNGL from pressurized natural gas comprising predominantly nitrogen withsmaller amounts of methane, C₂₊ hydrocarbons and helium.

The pressurized natural gas is usually extracted from an undergroundsource, such as a geological deposit or a natural gas field. The naturalgas is typically extracted at a pressure in the range from about 2 barto about 200 bar, preferably from about 10 bar to about 100 bar.

The composition of natural gas depends on the source. However, someembodiments of the present invention concern recovering valuablecomponents of nitrogen-rich natural gas, i.e. natural gas having a lowcalorific value, e.g. a calorific value of no more than 300 BTU/scf(“British thermal units/standard cubic foot”), i.e. about 11.2 MJ/sm³(“mega Joules/standard metre cubed” at 15° C.). The natural gascomprises at least about 70%, e.g. at least about 80% and preferably atleast about 90%, nitrogen. The nitrogen content of the pressurizednatural gas is usually no more than 99% and typically no more than 95%.

Other components of the natural gas suitable to be processed by thepresent invention include methane, helium and C₂₊ hydrocarbons,typically together with one or more impurities such as carbon dioxide,water and hydrogen sulfide.

Methane is typically present in the natural gas in an amount in therange from about 0.1% to about 30%, for example from about 0.1% to about20% or from about 0.1% to about 10%.

Helium is typically present in an amount in the range from about 0.01%to about 10%, for example from about 0.01% to about 5%.

C₂₊ hydrocarbons typically comprise C₂ to C₄ hydrocarbons, oftentogether with C₅ and C₆ hydrocarbons. Typical C₂₊ hydrocarbons includeone or more hydrocarbons selected from the group consisting of ethane(C₂), propane (C₃), butanes (C₄), pentanes (C₅) and hexanes (C₆). Thenatural gas typically comprises at least ethane, propane and butane. Thetotal amount of C₂₊ hydrocarbons in the natural gas is typically in therange of about 0.01% to about 5%.

The process may comprise extracting the pressurized natural gas from anunderground source and pre-treating the pressurized nitrogen-richnatural gas to remove one or more impurities incompatible with theprocess and thereby produce pre-treated natural gas.

Purities that are incompatible with the process include carbon dioxide,water and hydrogen sulfide. These impurities are incompatible because atleast a portion of the pressurized natural gas is cooled to a lowtemperature, typically below −100° C. At such cryogenic temperatures,these impurities freeze out of the gas causing blockages in pipework andchannels within heat exchangers, etc. Therefore, such “freezable”components are removed before the natural gas is cooled.

The impurities may be removed using conventional techniques. In thisregard, water may be removed in a selective adsorption process, e.g.using a zeolite adsorbent; and carbon dioxide and/or hydrogen sulfidemay be removed in an absorption process, e.g. using an amine such asmonoethanolamine.

The natural gas being pre-treated for impurity removal is typically at apressure in the range from about 2 bar to about 100 bar, for examplefrom about 40 bar to about 60 bar, e.g. about 50 bar. If the pressure ofthe natural gas after extraction is within this range, then the naturalgas could be pre-treated without pressure adjustment. If the pressure ofthe natural gas is significantly more than 100 bar, then the pressure ofthe natural gas would be reduced prior to undergoing the pre-treatment.

The pre-treated natural gas is cooled to produce cooled pre-treatednatural gas which is separated by distillation in the seconddistillation column system (i.e. an NGL recovery column system) toproduce NGL and C₂₊ hydrocarbon-depleted natural gas comprising heliumand methane.

The skilled person would appreciate that the temperature to which thepre-treated gas is cooled depends on the pressure and composition of thegas. With this data, it is possible to determine the temperature towhich the gas is cooled prior to being fed to the NGL recovery column.

The second distillation column system may comprise more than onedistillation column although, in preferred embodiments, the systemcomprises a single distillation column. The column may be trayed and/orpacked as required or as desired.

The second distillation column system usually operates at a pressurefrom about 2 bar to about 35 bar, for example from about 25 bar to 35bar, e.g. about 30 bar. In embodiments in which the pressure of thecooled pre-treated gas is within these ranges, the pre-treated gas couldbe fed to the second distillation column system without pressureadjustment. However, the pressure of the cooled pre-treated gas istypically substantially more than 35 bar. Therefore, the pressure of thecooled pre-treated gas is usually reduced prior to being fed to thesecond distillation column system.

Purification of Helium Product

The helium-enriched overhead vapor typically comprises at least 50%, forexample at least 65%, preferably at least 80%, e.g. about 90%, helium.The remainder of the helium-enriched overhead vapor is usuallypredominantly nitrogen.

The helium-enriched overhead vapor may be purified. In such embodiments,the process may comprise warming the helium-enriched overhead vapor byindirect heat exchange to produce helium-enriched gas; and purifying thehelium-enriched gas to produce pure helium gas. The purified helium gastypically comprises at least 99% helium.

The helium-enriched gas is typically purified by a pressure swingadsorption (PSA) process. Tail gas from the PSA process may be recycledto the first distillation column system after suitable pressure andtemperature adjustment.

If the feed gas contains hydrogen, the purification process may alsoinclude a catalytic oxidation step (e.g. a NIXOX unit). The catalyticoxidation step may be carried out upstream of the PSA, and the tail gasfrom the PSA recycled upstream of the feed pretreatment unit to removeresultant CO₂ and water, or to an intermediate point in the pretreatmentunit, such as between the CO₂ and water removal steps if only water wasproduced in the NIXOX unit, or water and only small amounts of CO₂ thatcan be removed in the water removal step, or it may be treatedseparately in a TSA system.

In embodiments in which liquid nitrogen is produced as product, at leasta portion of the liquid nitrogen may be used as a refrigerant in aprocess to liquefy the purified helium.

Recovery of Methane from Nitrogen-Enriched Bottoms Liquid

Where the feed gas comprises methane, methane is typically recoveredfrom nitrogen-enriched bottoms liquid as fuel gas and/or liquefiednatural gas (LNG). In such embodiments, the methane is typicallyseparated by distillation in a third distillation column system (i.e. amethane recovery column system) operating at elevated operatingpressure(s) to produce nitrogen overhead vapor and methane-enrichedbottoms liquid.

Methane-enriched bottoms liquid typically comprises at least 90%, forexample about 95%, methane. The bottoms liquid may be removed from theprocess without vaporization to form an LNG product. Additionally oralternatively, a portion of the methane-enriched bottoms liquid may bevaporized to produce fuel gas.

Nitrogen-enriched overhead vapor typically comprises at least 99%nitrogen. The nitrogen overhead vapor may be warmed by indirect heatexchange to produce warmed nitrogen gas. Additionally or alternatively,at least a portion of the nitrogen in the nitrogen-enriched overheadvapor is condensed and removed as liquid nitrogen. The liquid nitrogentypically comprises at least 99% nitrogen.

A portion of the nitrogen gas may recycled to the third distillationcolumn system after suitable pressure and temperature adjustment. Thenitrogen gas may be recycled from any point downstream of the thirddistillation column system, e.g. after warming, compression, coolingand/or expansion. Such a recycle can increase the refrigerationavailable to the process, and therefore increase the quantity of liquidproducts that can be made.

Additionally or alternatively, a portion of the nitrogen gas may beexpanded to produce expanded nitrogen gas, which is then warmed byindirect heat exchange to produce warmed expanded nitrogen gas. In suchembodiments, the nitrogen gas is usually work expanded in an expander toprovide refrigeration for the production of liquid from the process.

The third distillation column system may comprise a single distillationcolumn, or more than one distillation column in which each columnoperates at the same or different elevated pressures. In some preferredembodiments, the third distillation column system comprises a higherpressure distillation column (HP column) and a lower pressuredistillation column (LP column). The column(s) may be trayed and/orpacked as required or as desired.

The third distillation column system may comprise a condenser forcondensing overhead vapor. A portion of the condensed phase is typicallyreturned to the top of the column system as reflux. The condenser may bea stand alone unit, or in preferred embodiments, is a section in themain heat exchanger.

The or each elevated operating pressure of the third distillation columnsystem is typically less than the pressure of the bottoms liquid in thefirst distillation column system. Therefore, the process typicallycomprises expanding the bottoms liquid to the or one of the elevatedpressures of the third distillation column system prior to separation.

The third distillation column system typically operates at one or morepressures in the range from more than 1 bar to about 35 bar. Where thethird distillation column system comprises an HP column and an LPcolumn, the HP column typically operates at a pressure from about 20 barto about 35 bar, for example at about 25 bar, and the LP columntypically operates at a pressure from more than 1 bar to about 10 bar,for example about 1.5 bar. The pressure of the nitrogen-enriched bottomsliquid is adjusted as required prior to being fed to the methanerecovery column system.

In a first arrangement of the apparatus, there is comprised adistillation column system for operation at an elevated operatingpressure to separate at least partially condensed feed gas intohelium-enriched overhead vapor and nitrogen-enriched bottoms liquid; anoverhead condenser for partially condensing helium-enriched overheadvapor by indirect heat exchange to produce helium-enriched vapor asproduct and liquid for reflux in the column system; a first heatexchange system for cooling feed gas by indirect heat exchange with afirst nitrogen-enriched bottoms liquid to produce cooled feed gas andvapor for the column system; a first pressure reduction device forreducing the pressure of a second nitrogen-enriched bottoms liquid toproduce reduced pressure bottoms liquid; a second heat exchange systemfor cooling said cooled feed gas by indirect heat exchange against saidreduced pressure bottoms liquid to produce at least partially condensedfeed gas and at least partially vaporized bottoms liquid; and a secondpressure reduction device for reducing the pressure of said at leastpartially condensed feed gas to produce at least partially condensedfeed gas at reduced pressure for use as said feed to the distillationcolumn system.

The apparatus may comprise a separator to separate partially condensedoverhead vapor into helium-enriched vapor and liquid reflux.

Preferably, this arrangement comprises a third pressure reduction devicefor reducing the pressure of a third nitrogen-enriched bottoms liquid toproduce reduced pressure bottoms liquid for vaporization by indirectheat exchange in said overhead condenser to produce nitrogen-enrichedvapor.

These preferred arrangements usually comprise an expander for expandingsaid nitrogen-enriched vapor to produce expanded nitrogen-enriched vaporfor warming by indirect heat exchange in said overhead condenser toproduce warmed nitrogen-enriched vapor.

Preferably, this arrangement of the apparatus also comprises a fourthpressure reduction device for reducing the pressure of a fourth portionof said bottoms liquid to produce reduced pressure bottoms liquid forvaporization, optionally by said indirect heat exchange in said overheadcondenser to produce nitrogen-enriched vapor.

An alternative embodiment of the first arrangement of the apparatus maycomprise an expander for expanding said vaporized bottoms liquid toproduce expanded nitrogen-enriched vapor for warming by indirect heatexchange in said overhead condenser to produce warmed nitrogen-enrichedvapor.

In these embodiments, the apparatus preferably comprises a fourthpressure reduction device for reducing the pressure of a fourth portionof said nitrogen-enriched bottoms liquid to produce reduced pressurebottoms liquid; and a storage vessel for storing said reduced pressurebottoms liquid.

In a second arrangement of the apparatus, there is comprised adistillation column system for operation at an elevated operatingpressure to separate at least partially condensed feed gas intohelium-enriched overhead vapor and nitrogen-enriched bottoms liquid; anoverhead condenser for partially condensing helium-enriched overheadvapor by indirect heat exchange to produce helium-enriched vapor asproduct and liquid for reflux in the column system; a first pump forpumping a second nitrogen-enriched bottoms liquid to produce pumpedbottoms liquid; a first heat exchange system for cooling feed gas byindirect heat exchange with said pumped bottoms liquid to produce cooledfeed gas and nitrogen-enriched vapor; a second heat exchange system forcooling said cooled feed gas by indirect heat exchange against a firstnitrogen-enriched bottoms liquid to produce at least partially condensedfeed gas and vapor for the column system; and a pressure reductiondevice for reducing the pressure of said at least partially condensedfeed gas to produce at least partially condensed feed gas at reducedpressure for use as said feed to the distillation column system.

Preferably, this arrangement comprises a third pressure reduction devicefor reducing the pressure of a third portion of said bottoms liquid toproduce reduced pressure bottoms liquid for vaporization by indirectheat exchange in said overhead condenser to produce nitrogen-enrichedvapor.

These preferred arrangements usually comprise an expander for expandingsaid nitrogen-enriched vapor to produce expanded nitrogen-enriched vaporfor warming by indirect heat exchange in said overhead condenser toproduce warmed nitrogen-enriched vapor.

Preferably, this arrangement of the apparatus also comprises a fourthpressure reduction device for reducing the pressure of a fourth portionof said bottoms liquid to produce reduced pressure bottoms liquid forvaporization by indirect heat exchange in said overhead condenser toproduce nitrogen-enriched vapor.

The or each heat exchange system may be an independent unit. In otherembodiments, the two or more heat exchange systems may be differentsections of a single heat exchange unit. In preferred embodiments, allof the heat exchange systems identified above are different sections ofa primary (or main) heat exchanger.

The invention will now be further described with reference to thecomparative process depicted in FIG. 1 and the embodiments of thepresent invention depicted in FIGS. 2 to 9.

The comparative process depicted in FIG. 1 is based on the processdisclosed in U.S. Pat. No. 5,167,125 integrated with a main heatexchanger 92 and with a gaseous feed comprising 93% nitrogen, 5% methaneand 2% helium. The feed is at a temperature of about 49° C. and apressure of 30 bar.

A stream 90 of feed gas is cooled by indirect heat exchange in the mainheat exchanger 92 to form a stream 100 of cooled gas. The cooled gas isfed to reboiler 108 of distillation column 102 where it is furthercooled by indirect heat exchange against bottoms liquid in the column toform a stream 110 of further cooled feed. A small amount (˜11%) of thefeed is condensed. Stream 110 is then expanded across valve 112 to about25 bar and the expanded stream 113 fed to the distillation column whereit is separated into nitrogen-enriched bottoms liquid andhelium-enriched overhead vapor.

A stream 104 of bottoms liquid is removed from the column 102, expandedacross valve 122 to about 1.5 bar and then used to partially condenseoverhead vapor from the column 102 by indirect heat exchange. In thisregard, a stream 114 of overhead vapor is fed to condenser 116 where itis partially condensed by indirect heat exchange against vaporizingbottoms liquid to produce liquid reflux 120 for the column and a stream118 of crude helium gas which is warmed by indirect heat exchange in themain heat exchanger 92, thereby producing a stream 119 of warmed heliumgas (˜90%) containing nitrogen (˜10%).

A stream 126 of nitrogen-enriched bottoms liquid vaporized by thecondensing overhead vapor is then used to cool the feed by indirect heatexchange in the main heat exchanger 92 to produce stream 128 of warmednitrogen gas (˜95%) containing methane (˜5%).

All of the refrigeration for the comparative process depicted in FIG. 1is provided by Joule-Thomson expansion.

In this example, there is no liquid product 124 from the boiling side ofthe condenser 116. Heat balance means that, because all of the feed isin the gaseous phase and no significant refrigeration is provided, allof the products must also be in the gaseous phase.

FIG. 2 depicts an improved process over FIG. 1. Common features havebeen given the same reference numerals. The following is a discussion ofthe new features.

FIG. 2 depicts a process according to the invention where stream 100 isgaseous or two phase. The feed is fully, or almost fully, condensed inheat exchanger 136 which is cooled by boiling a stream 168 ofhelium-free bottoms liquid at elevated pressure. In this regard, aportion 164 of the bottoms liquid is expanded across valve 166 and fedas stream 168 to the heat exchanger 136 to form stream 170 of vaporizedbottoms liquid. Additional refrigeration is provided by expanding stream170 in expander 174 and using the expanded stream to help cool the feed90 in the main heat exchanger 92. A stream 172 of warmed nitrogen gas isthen removed from the heat exchanger and may be purified.

An advantage of the process of FIG. 2 over the comparative processdepicted in FIG. 1 is that because of the additional condensation of thefeed in heat exchanger 136, the vapor part of the feed and therefore thevapor flow in the column 102 above the feed location is reducedsignificantly leading to a reduction in the diameter of that section ofthe column.

FIG. 3 depicts an improved process over FIG. 2. Common features havebeen given the same reference numerals. The following is a discussion ofthe new features.

In FIG. 3, a further portion 132 of helium-free bottoms liquid isexpanded across valve 133 and the expanded stream 134 is fed to theoverhead condenser 116 where it is boiled and superheated at anintermediate pressure. Stream 138 of vaporized bottoms liquid isexpanded in expander 140 and the expanded stream 142 and reheated incondenser 116 to produce a stream 144 of reheated nitrogen gas which isused to help cool the feed 90 in the main heat exchanger 92. Stream 146of the resultant nitrogen gas is taken from the heat exchanger 92 and isavailable as a product or for further purification.

Stream 170 is used without expansion to cool the feed 90 in the mainheat exchanger 92.

An advantage of the process of FIG. 3 over the process depicted in FIG.2 is that refrigeration is integrated with the separation process, andthe amount of product available at pressure is increased.

FIG. 4 depicts a modified process of FIG. 3 in which the feed pressureis greater. Common features have been given the same reference numerals.The following is a discussion of the new features.

Stream 164 of helium-free bottoms liquid is pumped in pump 165 toproduce a stream 168 of pumped bottoms liquid which is used to cool thefeed in heat exchanger 169 upstream of the column reboiler 108. Therefrigeration provided by the expander 140 offsets the energy input tothe process of the pump 168.

FIG. 5 depicts a preferred process in which most of the nitrogen productis boiled and expanded to provide refrigeration for production of someof the nitrogen product as liquid.

Feed 90 is cooled initially by indirect heat exchange in the main heatexchanger 92 to produce stream 100 and then subsequently further cooledand condensed by indirect heat exchange in the column reboiler 108 andheat exchanger 136. Stream 111 of condensed feed is expanded acrossvalve 112 and fed to column 102 for distillation. The column 102 isreboiled by the feed in reboiler 108, and nitrogen in the overhead vaporis condensed in condenser 116 to provide reflux 120 for the column 102.A stream 118 of impure helium gas is removed from the condenser 116 andwarmed against the feed 90 in the main heat exchanger 92 to produce ahelium gas stream 119 suitable for purification by PSA or by some othermeans.

A first portion of the helium-free bottoms liquid 104 is boiled in thebottom of column 102 to provide vapor for the column.

A second portion 132 of helium-free bottoms liquid 104 is expandedacross valve 133 and the expanded stream 134 is used to cool andcondense the feed by indirect heat exchange in heat exchanger 136. Astream 138 of vaporized bottoms liquid is work expanded in expander 140to produce expanded stream 142 which is then fed to the overheadcondenser 116 to condense nitrogen in the overhead vapor for reflux 120.Stream 144 of nitrogen gas is then fed to the main heat exchanger 92 tohelp cool the feed 90, thereby producing a stream 146 of impure nitrogengas suitable for further purification.

A third portion of helium-free bottoms liquid 104 is expanded acrossvalve 122 to produce expanded stream 105 which is fed to the overheadcondenser 116 to help condense nitrogen in the overhead vapor. Stream126 of nitrogen gas is then fed to the main heat exchanger 92 to helpcool the feed 90, thereby produce another stream 128 of impure nitrogengas suitable for further purification.

A fourth portion 180 of helium-free bottoms liquid 104 is expandedacross valve 182 to form a two phase stream 184 which is fed to astorage tank 185 where it is separated into a liquid stream 186 and avapor stream 188. Liquid stream 186 could be vaporized to providerefrigeration, for example in a downstream helium liquefier, or exportedas a product, for example for f racking. The vapor stream 188 is used tohelp cool the feed 90 in the main heat exchanger 92 to produce a furtherstream 190 of impure nitrogen gas suitable for further purification.

FIG. 6 depicts a modified process of FIG. 5 in which liquid product issubcooled in condenser 116. Common features have been given the samereference numerals. The following is a discussion of the new features.

The fourth portion 180 of helium-free bottoms liquid is fed withoutexpansion to the condenser 116 where it is subcooled to form stream 181of subcooled bottoms liquid. Stream 182 is expanded across valve 182 toproduce expanded stream 184 which is two phase. Stream 184 is fed to thestorage tank 185 where it is separated into the liquid stream 186 andthe vapor stream 188.

If the feed contains C₂₊ hydrocarbons, a hydrocarbon (NGL) recoverycolumn may be added upstream of the helium separation column 102, asillustrated in FIG. 7.

Feed 90 is cooled in the main heat exchanger 92 and divided into a firstportion 191 and a second portion. The first portion 191 is work expandedin expander 192 and the expanded stream 193 is fed back to the main heatexchanger 92 where it is further cooled to produce stream 194 which isfed to an intermediate location in an NGL recovery column 96. The secondportion is further cooled and condensed by indirect heat exchange in themain heat exchanger to form stream 196 of liquid feed which is expandedacross valve 94 to produce expanded feed stream 198 which is fed to thetop of the NGL recovery column 96.

The feeds to the column 96 are separated into C₂₊ hydrocarbon bottomsliquid, removed as stream 199, and C₂₊ hydrocarbon-depleted overheadvapor. Column 96 is reboiled in reboiler 98 using an external heatsource such as steam, hot oil or cooling water.

A stream 100 of overhead vapor is removed from column 96 and used toreboil the helium recovery column 102 to produce a stream 110 of cooledand partially condensed overhead vapor. Stream 110 is further cooled andcondensed in heat exchanger 136 by indirect heat exchange againsthelium-free bottoms liquid 134 from column 102. The further condensedstream 111 is then expanded across valve 112 and fed as stream 113 tocolumn 102 where it is separated into nitrogen-enriched bottoms liquidand helium-enriched overhead vapor.

A stream 114 of helium-enriched overhead vapor is taken from column 102and nitrogen in the vapor is condensed by indirect heat exchange in heatexchanger 116 to form a two phase stream 115 that is separated in phaseseparator 103. A stream 120 of nitrogen-enriched liquid is used toprovide reflux to column 102. A stream 118 of impure helium gas iswarmed by indirect heat exchange in heat exchanger 116 to form stream121 of warmed helium gas which is then used to help cool the feed 90 byindirect heat exchange in the main heat exchanger 92. The stream 119 ofimpure helium gas from the main heat exchanger 92 is suitable forpurification by PSA or by some other means.

A first portion of the helium-free bottoms liquid 104 is boiled in thebottom of column 102 to provide vapor for the column.

A second portion of nitrogen-enriched bottoms liquid 104 is expandedacross valve 122 and the expanded stream 105 is used to providerefrigeration duty in heat exchanger 116. The resultant stream 126 ofvaporized liquid is then used to help cool the feed 90 by indirect heatexchange in the main heat exchanger 92 to produce a stream 128 of warmedimpure nitrogen gas suitable for further purification.

A third portion 132 of the helium-free bottoms liquid 104 is expandedacross valve 133 and then used to provide refrigeration duty in heatexchanger 136. The stream 137 of impure nitrogen gas is then removedfrom heat exchanger 136 and fed to the main heat exchanger 92 where ishelps cool the feed 90. A stream 138 of warmed impure nitrogen gas isthen work expanded in expander 140 and the expanded stream 142 is usedto provide refrigeration duty in heat exchanger 116. The resultantstream 144 of impure nitrogen gas is then used to help cool the feed inthe main heat exchanger 92.

A fourth portion 180 of the helium-free bottoms liquid is subcooled inheat exchanger 116 and the resultant stream 181 is expanded across valve182 to form a two phase stream 184 which is fed to a storage tank 185from which a stream 186 of liquid nitrogen may be removed. A stream 188of impure nitrogen gas is taken from the storage tank 185 and used tohelp cool the feed 90 by indirect heat exchange in the main heatexchanger 92. Stream 190 of warmed impure nitrogen gas is suitable forfurther purification.

If pure nitrogen and/or a fuel stream are required, the helium-depletedbottoms liquid from the helium recovery column may be separated beforeand/or after work expansion, as illustrated in FIG. 8.

The feed 90 is cooled initially by indirect heat exchange in the mainheat exchanger 92 and then further cooled and condensed by indirect heatexchange in the reboiler 108 of the helium recovery column 102 and heatexchanger 136. The condensed stream 111 is expanded across valve 112 andthen fed as stream 113 to the column 102 where it is separated intohelium-enriched overhead vapor and nitrogen-enriched bottoms liquid.

Overhead vapor is removed as stream 114 and nitrogen in the stream iscondensed by indirect heat exchange in heat exchanger 116 to form atwo-phase stream 115 which is phase separated in phase separator 103.The liquid portion 120 is fed back to the top of the column 102 asreflux. The vapor portion 118 is used to help cool the overhead vapor inheat exchanger 116 and is then further warmed in the main exchanger 92against the cooling feed 90. The resultant stream 119 of helium gas issuitable for further purification.

A portion 132 of the bottoms liquid 104 is expanded across valve 133 andthe expanded stream 134 is warmed by indirect heat exchange in heatexchanger 136 before being fed as stream 200 to a first nitrogenpurification column 208. The feed 200 is separated into methane-enrichedbottoms liquid and nitrogen-enriched overhead vapor.

Overhead vapor 230 is condensed by indirect heat exchanger againstexpanded bottoms liquid 214 in overhead condenser 232 to produce reflux234 for the column 208, and a stream 130 of liquid nitrogen. Stream 130is cooled by indirect heat exchange in heat exchanger 136 and the cooledstream 180 is subcooled in heat exchanger 116. Subcooled stream 181 isexpanded across valve 182 and the expanded stream 184 is fed to storagetank 185. A stream 186 of pure nitrogen liquid can be removed from tank185. Vapor 188 from the tank is used to help cool the feed 90 in themain heat exchanger 92 to produce stream 190 of nitrogen gas.

A stream 210 of bottoms liquid is expanded across valve 212 and theexpanded stream 214 is fed to the overhead condenser for refrigerationduty. Vaporized bottoms liquid is removed from the overhead condenser232 as stream 216. Unvaporized bottoms liquid is removed as stream 218,vaporized by indirect heat exchange in heat exchanger 136 and thevaporized stream 220 is combined with stream 216 to form combined stream222 which is used to help cool the feed 90 in the main heat exchanger 92and then work expanded in expander 140. The expanded stream 142 is thenfed to a second nitrogen purification column 258 operating at a lowerpressure than the first nitrogen purification column 208.

A second portion 250 of bottoms liquid 104 from the helium recoverycolumn 102 is subcooled by indirect heat exchange in heat exchanger 116and the subcooled liquid 252 is expanded across valve 254 and theexpanded stream 256 is fed to the top of the second nitrogenpurification column.

The feeds to the second nitrogen purification column 258 are separatedinto methane-enriched bottoms liquid and nitrogen-enriched overheadvapor. A first portion 262 of the methane-enriched bottoms liquid isreboiled in heat exchanger 116 and fed back to the column 258 to providevapor for the distillation. A second portion 270 of the bottoms liquidis pumped in pump 272 and the pumped stream 274 is used to help cool thefeed 90 in the main heat exchanger 92 to produce a stream 276 of fuelgas.

A stream 226 of nitrogen vapor is warmed in heat exchangers 116 and 92to provide a vent gas stream 146.

FIG. 9 depicts a fully integrated scheme with NGL recovery, HP and LPcolumns and liquid nitrogen production from an underground gas source,and helium purification by PSA to produce a stream 302 pure helium thatcan be fed directly to a helium liquefier.

Feed gas 70 from an underground source is pre-treated 72 to removedwater and carbon dioxide to produce stream 90 of dry, CO₂-free feed gaswhich is cooled by indirect heat exchange in the main heat exchanger 92.A first portion 191 of the cooled feed is expanded in expander 192 toproduce a two phase stream 193 which is phase separated in separator 95.The liquid phase 197 is fed directly to an NGL recovery column 96. Thevapor phase 195 is cooled in the main heat exchanger 92 and the cooledstream 194 is also fed to the NGL recovery column 96. A second portionof the cooled feed is further cooled in the main heat exchanger 92,expanded in valve 94 and fed to the column 96 as reflux stream 198.

The feeds to the NGL column 96 are separated into a C₂₊-enriched bottomsliquid and C₂₊-depleted overhead vapor. The bottoms liquid is reboiledwith external heat in reboiler 98 to provide vapor for the separation,and an NGL stream 199 is removed. Further vapor (stream 402) for thecolumn 96 is provided by reboiling a stream 400 of liquid taken from anintermediate location of the column 96 in the main heat exchanger 92.

A stream 100 of overhead vapor is cooled and condensed in the main heatexchanger 92 by indirect heat exchange against reboiling helium-freebottoms liquid 410 and expanded bottoms liquid 204 from the heliumrecovery column 102. The condensed feed 111 is then expanded acrossvalve 112 and the expanded stream 113 fed to the helium recovery column102 where it is separated into the helium-free bottoms liquid andhelium-enriched overhead vapor.

A stream 114 of overhead vapor is fed to the main heat exchanger 92where nitrogen in the stream in condensed to form a two phase stream 115which is phase separated in separator 103. The liquid phase 120 is fedas reflux to the helium recovery column 102. The vapor phase 118 is usedto help cool the feed 90 in the main heat exchanger 92 and the resultantwarmed stream 119 is fed to a helium PSA unit 300 which produces astream 302 of pure helium. A stream 304 of tail gas from the PSA unit300 is compressed in compressor 306 and the compressed stream 308 iscooled by indirect heat exchange in aftercooler 310 and the main heatexchanger 92 before being recycled as stream 314 to the helium recoverycolumn 102.

After cooling the feed to the helium recovery column 102, a portion ofthe expanded helium-free bottoms liquid is fed as stream 200 from themain heat exchanger to a first nitrogen purification column 208 where itis separated into methane-enriched bottoms liquid and nitrogen-enrichedoverhead vapor.

A stream 230 of nitrogen-enriched overhead vapor is condensed byindirect heat exchange in the main heat exchanger. A portion 234 of thecondensed stream is fed to the first nitrogen purification column asreflux. The remaining portion is cooled by indirect heat exchange in themain heat exchanger 92 and the cooled stream 181 expanded across valve182 to form two phase stream 184. Stream 184 is fed to a storage tank185 from which a stream 186 of liquid nitrogen may be taken. Vaporstream 188 is warmed in the main heat exchanger 92 to produce nitrogengas stream 190.

A stream 210 of methane-enriched bottoms liquid is expanded across valve212 and expanded stream 214 is warmed and vaporized by indirect heatexchange in the main heat exchanger 92. Gaseous stream 138 is expandedin expander 140 and the expanded stream is fed to a second nitrogenpurification column 258. Reflux to the second nitrogen purificationcolumn 258 is provided by a portion 252 of the expanded bottoms liquid204 from the helium recovery column 102. Stream 252 is expanded acrossvalve 254 and fed as reflux stream 256 to the column 258.

The feeds to the second nitrogen purification column are separated intomethane-enriched bottoms liquid and nitrogen-enriched overhead vapor.The column is reboiled by vaporizing a stream 260 of bottoms liquid inthe main heat exchanger 92. A stream 270 of bottoms liquid is pumped inpump 272 and pumped stream 274 is used to help cool the feed 90 in themain heat exchanger 92 to produce fuel gas stream 276.

A stream 226 of overhead vapor is warmed by indirect heat exchange inthe main heat exchanger 92 and divided into two portions, streams 147and 280. Stream 147 may be a product stream but it is usually vented.Stream 280 is compressed in compressor 282 and the compressed stream 284is cooled in aftercooler 286. The cooled stream 288 is cooled in themain heat exchanger 92 before being combined with stream 214 after ithas been vaporized to form combined stream 138 from the first nitrogenpurification column 208 to the second nitrogen purification column 258.

Aspects of the present invention include:

#1. A process for recovering helium from a nitrogen-rich feed gascomprising helium, said process comprising:

-   -   cooling a pressurized nitrogen-rich feed gas comprising helium        to produce cooled feed; and    -   separating said feed in a first distillation column system        operating at an elevated operating pressure to produce        helium-enriched overhead vapor and nitrogen-enriched bottoms        liquid(s);        wherein said feed to the first distillation column system is at        least partially condensed; and        wherein said cooling of said feed gas is achieved by indirect        heat exchange against at least a first nitrogen-enriched bottoms        liquid at a first elevated pressure and a second        nitrogen-enriched bottoms liquid at a second elevated pressure        that is different from said first elevated pressure.        #2. A process according to aspect #1, wherein said first        elevated pressure is equal to the elevated operating pressure of        said first distillation column system.        #3. A process according to aspect #1 or aspect #2, wherein said        first elevated pressure is from about 2 bar to about 35 bar.        #4. A process according to any of aspects #1 to #3, wherein the        second elevated pressure is less than the elevated operating        pressure of said first distillation column system.        #5. A process according to aspect #4, wherein the second        elevated pressure is from about 1 bar to about 30 bar.        #6. A process according to aspect #4 or aspect #5 comprising        expanding bottoms liquid to produce said second bottoms liquid.        #7. A process according to any of aspects #1 to #6, wherein said        feed gas is at subcritical pressure.        #8. A process according to aspect #7, wherein said feed gas is        cooled by indirect heat exchange against said first bottoms        liquid and then at least partially condensed by indirect heat        exchange against said second bottoms liquid.        #9. A process according to any of aspects #1 to #3, wherein the        second elevated pressure is greater than the elevated operating        pressure of said first distillation column system.        #10. A process according to aspect #9, wherein the second        elevated pressure is from about 3 bar to about 150 bar.        #11. A process according to #9 or #10 comprising pumping bottoms        liquid to produce said second bottoms liquid.        #12. A process according to any of aspects #1 to #3 and #9 to        #11, wherein said feed gas is at supercritical pressure.        #13. A process according to aspect #12, wherein said feed gas is        cooled by indirect heat exchange against said first bottoms        liquid and then further cooled by indirect heat exchange against        said second bottoms liquid.        #14. A process according to aspect #12, comprising expanding        said cooled feed prior to feeding said cooled feed to said first        distillation column system.        #15. A process according to any of aspects #1 to #14, wherein        the feed to the first distillation column system has a vapor        fraction of no more than 0.5.        #16. A process according to any of aspects #1 to #15, wherein        the feed to the first distillation column system is at least        substantially fully condensed.        #17. A process according to any of aspects #1 to #16, wherein        said pressurized nitrogen-rich feed gas is at a pressure greater        than said elevated operating pressure of said first distillation        column, said process comprising expanding said at least        partially condensed feed prior to separation.        #18. A process according to any of aspects #1 to #17, wherein        the pressure of said pressurized nitrogen-rich feed gas is from        about 2 bar to about 200 bar.        #19. A process according to any of aspects #1 to #18, wherein        said elevated operating pressure of the distillation column        system is from about 2 bar to about 35 bar.        #20. A process according to any of aspects #1 to #19 comprising        expanding vaporized bottoms liquid, or a fluid derived        therefrom, to produce expanded nitrogen-enriched gas and using        said expanded gas to provide a part of the refrigeration duty of        the process.        #21. A process according to any of aspects #1 to #20, wherein        said second bottoms liquid is at least partially vaporized as a        result of said indirect heat exchange against said feed gas,        said process comprising:    -   warming said vaporized bottoms liquid by indirect heat exchange        to produce warmed nitrogen-enriched gas; and    -   expanding said warmed nitrogen-enriched gas to produce expanded        nitrogen-enriched gas; and    -   cooling said feed gas by indirect heat exchange with said        expanded nitrogen-enriched gas to produce cooled feed gas.        #22. A process according to any of aspects #1 to #21 comprising:    -   expanding a third bottoms liquid to produce expanded        nitrogen-enriched fluid;    -   vaporizing said expanded nitrogen-enriched fluid by indirect        heat exchange against condensing nitrogen in said first        distillation column system to produce nitrogen-enriched gas;    -   expanding said nitrogen-enriched gas to produce expanded        nitrogen-enriched gas; and    -   condensing nitrogen gas in said first distillation column system        by indirect heat exchange against said expanded        nitrogen-enriched gas to produce liquid reflux for said first        distillation column system.        #23. A process according to aspect #22 comprising:    -   expanding a fourth bottoms liquid to produce further expanded        nitrogen-enriched fluid; and    -   vaporizing said further expanded nitrogen-enriched fluid by        indirect heat exchange against condensing nitrogen in said first        distillation column system to produce further nitrogen-enriched        gas.        #24. A process according to any of aspects #1 to #20, wherein        said second bottoms liquid is vaporized as a result of said        indirect heat exchange against said feed gas, said process        comprising:    -   expanding said vaporized bottoms liquid to produce expanded        nitrogen-enriched gas; and    -   condensing nitrogen gas in said first distillation column system        by indirect heat exchange with said expanded nitrogen-enriched        gas to produce liquid reflux for said first distillation column        system and warmed nitrogen-enriched gas.        #25. A process according to #24 comprising:    -   expanding a third bottoms liquid to produce further expanded        nitrogen-enriched fluid; and    -   vaporizing said further expanded nitrogen-enriched fluid by        indirect heat exchange against condensing nitrogen in said first        distillation column system to produce further nitrogen-enriched        gas.        #26. A process according to aspect #24 or aspect #25 comprising        expanding a fourth bottoms liquid to form an expanded fluid; and        separating said expanded fluid into a vapor phase and a liquid        phase.        #27. A process according to aspect #26, wherein said vapor phase        is warmed by indirect heat exchange to produce a gaseous        nitrogen product.        #28. A process according to aspect #26 of #27, comprising        sub-cooling said fourth bottoms liquid prior to expansion to        form said expanded two phase fluid.        #29. A process according to aspect #28, wherein said fourth        bottoms liquid is sub-cooled by indirect heat exchange against        expanded nitrogen-enriched gas        #30. A process according to any of aspects #1 to #29, wherein        the process is autorefrigerated.        #31. A process according to any of aspects #1 to #30, wherein        said feed gas is taken from a natural gas liquids (NGL) recovery        column.        #32. A process according to any of aspects #1 to #31 comprising:    -   cooling and at least partially condensing pressurized dry,        carbon dioxide-free natural gas to produce at least partially        condensed natural gas; and    -   separating said at least partially condensed natural gas in a        second distillation column system operating at an elevated        operating pressure to produce C₂₊-depleted overhead vapor and        C₂₊-enriched bottoms liquid,        wherein said C₂₊-depleted overhead vapor is said nitrogen-rich        feed gas.        #33. A process according to aspect #32, wherein said natural gas        comprises at least 70% nitrogen (N₂).        #34. A process according to aspect #32 or aspect #33, wherein        said pressurized dry, carbon dioxide-free natural gas is at a        pressure of from about 2 bar to about 200 bar.        #35. A process according to any of aspects #32 to #34, wherein        said elevated pressure of said second distillation column system        is less than the pressure of said pressurized dry, carbon        dioxide-free natural gas, said process comprising expanding said        at least partially condensed natural gas to said elevated        pressure of said second distillation column system prior to        separation.        #36. A process according to any of aspects #32 to #34, wherein        said elevated operating pressure of said second distillation        column system is from about 2 bar to about 35 bar.        #37. A process according to any of aspects #1 to #36 comprising:    -   warming said helium-enriched overhead vapor by indirect heat        exchange to produce helium-enriched gas; and    -   purifying said helium-enriched gas to produce pure helium gas.        #38. A process according to aspect #37, wherein said        helium-enriched gas is purified by a pressure swing adsorption        (PSA) process.        #39. A process according to aspect #38, wherein tail gas from        said PSA process is recycled to said first distillation column        system after suitable pressure and temperature adjustment.        #40. A process according to any of aspects #1 to #39, wherein        said feed gas comprises methane, said process comprising        recovering methane from said bottoms liquid to produce fuel gas        or LNG.        #41. A process according to any of aspects #1 to #40 comprising        separating bottoms liquid in a third distillation column system        operating at elevated operating pressure(s) to produce nitrogen        overhead vapor and methane-enriched bottoms liquid.        #42. A process according to aspect #41 comprising warming said        nitrogen overhead vapor by indirect heat exchange to produce        warmed nitrogen gas.        #43. A process according to aspect #41 or aspect #42 comprising        recycling a portion of said nitrogen gas to said third        distillation column system after suitable pressure and        temperature adjustment.        #44. A process according to aspect #42 comprising expanding a        portion of said nitrogen gas to produce expanded nitrogen gas,        and warming said expanded nitrogen gas by indirect heat exchange        to produce warmed expanded nitrogen gas.        #45. A process according to any of aspects #41 to #44 comprising        warming and evaporating said methane-enriched bottoms liquid by        indirect heat exchange to produce fuel gas.        #46. A process according to any of aspects #41 to #45, wherein        said third distillation column system additionally produces a        nitrogen-enriched overhead vapor, said process comprising        condensing said nitrogen-enriched overhead vapor to produce        condensed vapor and removing a portion of said condensed vapor        as a liquid nitrogen product.        #47. A process according to any of aspects #41 to #46, wherein        the or each elevated pressure of said third distillation column        system is less than the pressure of the bottoms liquid, said        process comprising expanding said bottoms liquid to the or one        of the elevated pressures of said third distillation column        system prior to separation.        #48. A process according to any of aspects #41 to #47, wherein        said elevated pressure of said third distillation column system        is from more than 1 bar to about 35 bar.        #49. A process substantially as described herein with reference        to the examples and/or drawings.        #50. Apparatus for recovering helium from a nitrogen-rich feed        gas comprising helium, said apparatus comprising:    -   a distillation column system for operation at an elevated        operating pressure to separate at least partially condensed feed        gas into helium-enriched overhead vapor and nitrogen-enriched        bottoms liquid(s);    -   an overhead condenser for partially condensing helium-enriched        overhead vapor by indirect heat exchange to produce        helium-enriched vapor as product and liquid for reflux in the        column system;    -   a first heat exchange system for cooling feed gas by indirect        heat exchange with a first nitrogen-enriched bottoms liquid to        produce cooled feed gas and vapor for the column system;    -   a first pressure reduction device for reducing the pressure of a        second nitrogen-enriched bottoms liquid to produce reduced        pressure bottoms liquid;    -   a second heat exchange system for cooling said cooled feed gas        by indirect heat exchange against said reduced pressure bottoms        liquid to produce at least partially condensed feed gas and        vaporized bottoms liquid; and    -   a second pressure reduction device for reducing the pressure of        said at least partially condensed feed gas to produce at least        partially condensed feed gas at reduced pressure for use as said        feed to the distillation column system.        #51. Apparatus according to aspect #50 comprising a third        pressure reduction device for reducing the pressure of a third        nitrogen-enriched bottoms liquid to produce reduced pressure        bottoms liquid for vaporization by indirect heat exchange in        said overhead condenser to produce nitrogen-enriched vapor.        #52. Apparatus according to aspect #51 comprising an expander        for expanding said nitrogen-enriched vapor to produce expanded        nitrogen-enriched vapor for warming by indirect heat exchange in        said overhead condenser to produce warmed nitrogen-enriched        vapor.        #53. Apparatus according to aspect #51 or aspect #52 comprising        a fourth pressure reduction device for reducing the pressure of        a fourth nitrogen-enriched bottoms liquid to produce reduced        pressure bottoms liquid for vaporization by indirect heat        exchange in said overhead condenser to produce nitrogen-enriched        vapor.        #54. Apparatus according to #50 comprising an expander for        expanding said vaporized bottoms liquid to produce expanded        nitrogen-enriched vapor for warming by indirect heat exchange in        said overhead condenser to produce warmed nitrogen-enriched        vapor.        #55. Apparatus according to #54 comprising:    -   a fourth pressure reduction device for reducing the pressure of        a fourth nitrogen-enriched bottoms liquid to produce reduced        pressure bottoms liquid; and    -   a storage vessel for storing said reduced pressure bottoms        liquid.        #56. Apparatus for recovering helium from a nitrogen-rich feed        gas comprising helium, said apparatus comprising:    -   a distillation column system for operation at an elevated        operating pressure to separate at least partially condensed feed        gas into helium-enriched overhead vapor and nitrogen-enriched        bottoms liquid(s);    -   an overhead condenser for partially condensing helium-enriched        overhead vapor by indirect heat exchange to produce        helium-enriched vapor as product and liquid for reflux in the        column system;    -   a first pump for pumping a second nitrogen-enriched bottoms        liquid to produce pumped bottoms liquid;    -   a first heat exchange system for cooling feed gas by indirect        heat exchange with said pumped bottoms liquid to produce cooled        feed gas and nitrogen-enriched vapor;    -   a second heat exchange system for cooling said cooled feed gas        by indirect heat exchange against a first nitrogen-enriched        bottoms liquid to produce at least partially condensed feed gas        and vapor for the column system; and    -   a pressure reduction device for reducing the pressure of said at        least partially condensed feed gas to produce at least partially        condensed feed gas at reduced pressure for use as said feed to        the distillation column system.        #57. Apparatus according to aspect #56 comprising a second        pressure reduction device for reducing the pressure of a third        nitrogen-enriched bottoms liquid to produce reduced pressure        bottoms liquid for vaporization by indirect heat exchange in        said overhead condenser to produce nitrogen-enriched vapor.        #58. Apparatus according to aspect #57 comprising an expander        for expanding said nitrogen-enriched vapor to produce expanded        nitrogen-enriched vapor for warming by indirect heat exchange in        said overhead condenser to produce warmed nitrogen-enriched        vapor.        #59. Apparatus according to aspect #57 or aspect #58 comprising        a third pressure reduction device for reducing the pressure of a        fourth nitrogen-enriched bottoms liquid to produce reduced        pressure bottoms liquid for vaporization by indirect heat        exchange in said overhead condenser to produce nitrogen-enriched        vapor.        #60. Apparatus substantially as described herein with reference        to the accompanying examples and/or drawings.

Comparative Example 1

A computer simulation of the process depicted in FIG. 1 has been carriedout using Aspen Plus (version 7.2, ©Aspen Technology Inc.). Theresultant heat and mass balance data for the key streams is presented inTable 1.

TABLE 1 90 100 104 105 106 110 111 114 118 119 124 Temperature C. 48.9−144.5 −151.8 −191.4 −147.3 −154.5 −189.3 45.2 Pressure bar 30.0 30.025.0 1.5 30.0 25.0 25.0 25.0 Molar Flow kmol/s 0.278 0.278 0.272 0.2720.000 0.278 0.000 0.169 0.006 0.006 Vapor Fraction 1.00 1.00 0.00 0.490.89 1.00 1.00 1.00 Mole fraction Nitrogen 0.9300 0.9300 0.9489 0.94890.9300 0.9590 0.1000 0.1000 Mole fraction Methane 0.0500 0.0500 0.05110.0511 0.0500 0.0020 0.0000 0.0000 Mole fraction Helium 0.0200 0.02000.0000 0.0000 0.0200 0.0390 0.9000 0.9000 126 128 Temperature C. −184.145.2 Pressure bar 1.5 1.5 Molar Flow kmol/s 0.272 0.272 Vapor Fraction1.00 1.00 Mole fraction Nitrogen 0.9489 0.9489 Mole fraction Methane0.0511 0.0511 Mole fraction Helium 0.0000 0.0000 Product recompression2899 kW Total 2899 kW

The power to recompress the product 128 to the feed pressure of 30 baris 2899 kW.

Example 1

A computer simulation of the process depicted in FIG. 2 has been carriedout using Aspen Plus. The resultant heat and mass balance data for thekey streams is presented in Table 2.

TABLE 2 90 100 104 105 106 110 111 114 118 119 124 Temperature C. 48.9−142.8 −151.8 −191.4 −147.3 −155.5 −158.8 −189.3 46.9 Pressure bar 30.030.0 25.0 1.5 30.0 30.0 25.0 25.0 25.0 Molar Flow kmol/s 0.278 0.2780.272 0.036 0.278 0.278 0.031 0.006 0.006 0.000 Vapour Fraction 1.001.00 0.00 0.49 0.90 0.04 1.00 1.00 1.00 Mole fraction Nitrogen 0.93000.9300 0.9489 0.9489 0.9300 0.9300 0.8150 0.1000 0.1000 Mole fractionMethane 0.0500 0.0500 0.0511 0.0511 0.0500 0.0500 0.0009 0.0000 0.0000Mole fraction Helium 0.0200 0.0200 0.0000 0.0000 0.0200 0.0200 0.18410.9000 0.9000 126 128 134 138 142 144 164 168 170 172 Temperature C.−160.8 46.9 −151.8 −157.5 −154.4 46.9 Pressure bar 1.5 1.5 25.0 18.618.6 18.2 Molar Flow kmol/s 0.036 0.036 0.236 0.236 0.236 0.236 VapourFraction 1.00 1.00 0.00 0.14 1.00 1.00 Mole fraction Nitrogen 0.94890.9489 0.9489 0.9489 0.9489 0.9489 Mole fraction Methane 0.0511 0.05110.0511 0.0511 0.0511 0.0511 Mole fraction Helium 0.0000 0.0000 0.00000.0000 0.0000 0.0000 Product recompression 806 kW Expander power −10 kWTotal 796 kW

In this example, only 13% of the helium-free product stream is boiled atlow pressure in the column condenser. Product stream 170 is boiled at18.6 bar and expanded to 18.2 bar in expander 174. The total power(mostly product recompression power for streams 128 and 172) is reducedby 73% from 2899 kW to 796 kW. In addition, because the vapour fractionof the feed is reduced, the vapor flow in the column above the feedlocation is reduced significantly leading to a reduction in the columndiameter.

Example 2

A computer simulation of the process depicted in FIG. 3 has been carriedout using Aspen Plus. The resultant heat and mass balance data for thekey streams is presented in Table 3.

TABLE 3 90 100 104 105 106 110 111 114 118 119 124 Temper- C. 48.9−140.7 −151.8 −191.4 −147.2 −158.9 −161.9 −189.3 46.8 ature Pressure bar30.0 30.0 25.0 1.5 30.0 30.0 25.0 25.0 25.0 Molar kmol/s 0.278 0.2780.272 0.007 0.278 0.278 0.019 0.006 0.006 Flow Vapour 1.00 1.00 0.000.49 0.92 0.02 1.00 1.00 1.00 Fraction Mole 0.9300 0.9300 0.9489 0.94890.9300 0.9300 0.7038 0.1000 0.1000 fraction Nitrogen Mole 0.0500 0.05000.0511 0.0511 0.0500 0.0500 0.0005 0.0000 0.0000 fraction Methane Mole0.0200 0.0200 0.0000 0.0000 0.0200 0.0200 0.2957 0.9000 0.9000 fractionHelium 126 128 134 138 142 144 146 164 168 170 172 Temper- C. −163.346.8 −174.8 −163.3 −187.1 −163.3 46.8 −151.8 −160.9 −155.5 46.8 aturePressure bar 1.5 1.5 6.4 6.4 1.5 1.5 1.5 25.0 15.4 15.4 15.4 Molarkmol/s 0.007 0.007 0.010 0.010 0.010 0.010 0.010 0.254 0.254 0.254 0.254Flow Vapour 1.00 1.00 0.36 1.00 0.96 1.00 1.00 0.00 0.20 1.00 1.00Fraction Mole 0.9489 0.9489 0.9489 0.9489 0.9489 0.9489 0.9489 0.94890.9489 0.9489 0.9489 fraction Nitrogen Mole 0.0511 0.0511 0.0511 0.05110.0511 0.0511 0.0511 0.0511 0.0511 0.0511 0.0511 fraction Methane Mole0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.00000.0000 fraction Helium Product recompression 788 kW Expander power  −8kW Total 779 kW

The advantage in this example is that the refrigeration is integratedwith the separation process, and the amount of product available atpressure is increased—only 6.3% of the product is at low pressure. Thetotal power consumption is also slightly reduced (by 2.1%) to 779 kW.

Example 3

A computer simulation of the process depicted in FIG. 4 has been carriedout using Aspen Plus. The resultant heat and mass balance data for thekey streams is presented in Table 4.

TABLE 4 90 100 104 105 106 110 111 114 118 119 124 Temper- C. 48.9−134.1 −151.8 −191.4 −144.0 −149.9 −157.2 −189.3 46.9 ature Pressure bar50.0 50.0 25.0 1.5 50.0 50.0 25.0 25.0 25.0 Molar kmol/s 0.278 0.2780.272 0.008 0.278 0.278 0.045 0.006 0.006 Flow Vapour 1.00 1.00 0.000.49 1.00 0.00 1.00 1.00 1.00 Fraction Mole 0.9300 0.9300 0.9489 0.94890.9300 0.9300 0.8711 0.1000 0.1000 fraction Nitrogen Mole 0.0500 0.05000.0511 0.0511 0.0500 0.0500 0.0013 0.0000 0.0000 fraction Methane Mole0.0200 0.0200 0.0000 0.0000 0.0200 0.0200 0.1276 0.9000 0.9000 fractionHelium 126 128 134 138 142 144 146 164 168 170 172 Temper- C. −159.346.9 −172.2 −159.3 −187.3 −159.3 46.9 −151.8 −149.2 −140.0 46.9 aturePressure bar 1.5 1.5 7.7 7.7 1.5 1.5 1.5 25.0 39.5 39.5 39.5 Molarkmol/s 0.008 0.008 0.038 0.038 0.038 0.038 0.038 0.226 0.226 0.226 0.226Flow Vapour 1.00 1.00 0.34 1.00 0.95 1.00 1.00 0.00 0.00 1.00 1.00Fraction Mole 0.9489 0.9489 0.9489 0.9489 0.9489 0.9489 0.9489 0.94890.9489 0.9489 0.9489 fraction Nitrogen Mole 0.0511 0.0511 0.0511 0.05110.0511 0.0511 0.0511 0.0511 0.0511 0.0511 0.0511 fraction Methane Mole0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.00000.0000 fraction Helium Product recompression 765 kW Expander power −35kW Pump power 28 kW Total 757 kW

In this case, part of the helium-free product 164 is increased inpressure in a pump 165 and used to cool the feed in heat exchanger 169upstream of the column reboiler 108. The refrigeration provided by theexpander offsets the energy input to the process in the pump. In theexample, the total power including recompression of the products back tothe feed pressure (50 bar in this case) is 757 kW.

Example 4

A computer simulation of the process depicted in FIG. 5 has been carriedout using Aspen Plus. The resultant heat and mass balance data for thekey streams is presented in Table 5.

TABLE 5 90 100 104 105 106 110 111 114 118 119 124 Temperature C. 48.9−122.4 −151.8 −191.4 −134.2 −150.9 −156.1 −189.3 46.9 Pressure bar 30.030.0 25.0 1.5 30.0 30.0 25.0 25.0 25.0 Molar Flow kmol/s 0.278 0.2780.272 0.005 0.278 0.278 0.066 0.006 0.006 Vapour 1.00 1.00 0.00 0.491.00 0.18 1.00 1.00 1.00 Fraction Mole fraction 0.9300 0.9300 0.94890.9489 0.9300 0.9300 0.9084 0.1000 0.1000 Nitrogen Mole fraction 0.05000.0500 0.0511 0.0511 0.0500 0.0500 0.0017 0.0000 0.0000 Methane Molefraction 0.0200 0.0200 0.0000 0.0000 0.0200 0.0200 0.0899 0.9000 0.9000Helium 126 128 134 138 142 144 146 164 168 170 172 Temperature C. −158.146.9 −156.3 −136.2 −188.3 −158.1 46.9 Pressure bar 1.5 1.5 19.8 19.8 1.51.5 1.5 Molar Flow kmol/s 0.005 0.005 0.215 0.215 0.215 0.215 0.215Vapour 1.00 1.00 0.12 1.00 0.93 1.00 1.00 Fraction Mole fraction 0.94890.9489 0.9489 0.9489 0.9489 0.9489 0.9489 Nitrogen Mole fraction 0.05110.0511 0.0511 0.0511 0.0511 0.0511 0.0511 Methane Mole fraction 0.00000.0000 0.0000 0.0000 0.0000 0.0000 0.0000 Helium 180 181 186 188 190Temperature C. −151.8 −194.2 −194.2 46.9 Pressure bar 25.0 1.1 1.1 1.1Molar Flow kmol/s 0.052 0.025 0.027 0.027 Vapour Fraction 0.00 0.00 1.001.00 Mole fraction Nitrogen 0.9489 0.8994 0.9957 0.9957 Mole fractionMethane 0.0511 0.1006 0.0043 0.0043 Mole fraction Helium 0.0000 0.00000.0000 0.0000 Product recompression 2957 kW Expander power −316 kW Total2640 kW Liquid production (1.1 bara) 59 TPD Power with no liquid(Example 3) 779 kW Additional power for Liquid 1861 kW Liquid specificpower 762 kWh/t

In the example, 9.2% of the product is produced as saturated liquid at1.1 bar. The total power including product recompression to 30 bar andnet of the power generation from the expander of 316 kW is 2342 kW. 59tonnes (t) per day of liquid is produced. Compared to Example 2, thetotal power is 1861 kW higher for the production of 59 tonnes per dayliquid, meaning that the specific power for the liquid production is 762kWh/t.

Example 5

A computer simulation of the process depicted in FIG. 6 has been carriedout using Aspen Plus. The resultant heat and mass balance data for thekey streams is presented in Table 6.

TABLE 6 90 100 104 105 106 110 111 114 118 119 124 Temperature C. 48.9−117.1 −151.8 −191.4 −130.0 −151.5 −156.4 −189.3 46.9 Pressure bar 30.030.0 25.0 1.5 30.0 30.0 25.0 25.0 25.0 Molar Flow kmol/ 0.278 0.2780.272 0.005 0.278 0.278 0.059 0.006 0.006 s Vapour Fraction 1.00 1.000.00 0.49 1.00 0.14 1.00 1.00 1.00 Mole fraction Nitrogen 0.9300 0.93000.9489 0.9489 0.9300 0.9300 0.8983 0.1000 0.1000 Mole fraction Methane0.0500 0.0500 0.0511 0.0511 0.0500 0.0500 0.0016 0.0000 0.0000 Molefraction Helium 0.0200 0.0200 0.0000 0.0000 0.0200 0.0200 0.1001 0.90000.9000 126 128 134 138 142 144 146 164 168 170 172 Temperature C. −156.546.9 −154.0 −132.0 −188.3 −156.5 46.9 Pressure bar 1.5 1.5 22.4 22.4 1.51.5 1.5 Molar Flow kmol/s 0.005 0.005 0.235 0.235 0.235 0.235 0.235Vapour Fraction 1.00 1.00 0.07 1.00 0.93 1.00 1.00 Mole fractionNitrogen 0.9489 0.9489 0.9489 0.9489 0.9489 0.9489 0.9489 Mole fractionMethane 0.0511 0.0511 0.0511 0.0511 0.0511 0.0511 0.0511 Mole fractionHelium 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 180 181 186 188190 Temperature C. −151.8 −186.8 −194.6 −194.6 46.9 Pressure bar 25.025.0 1.1 1.1 1.1 Molar Flow kmol/s 0.032 0.032 0.029 0.003 0.003 VapourFraction 0.00 0.00 0.00 1.00 1.00 Mole fraction Nitrogen 0.9489 0.94890.9442 0.9976 0.9976 Mole fraction Methane 0.0511 0.0511 0.0558 0.00240.0024 Mole fraction Helium 0.0000 0.0000 0.0000 0.0000 0.0000 Productrecompression 2935 kW Expander power −364 kW Pump power kW Total 2570 kWLiquid production (1.1 bara) 69 TPD Power with no liquid (Example 3) 779kW Additional power for Liquid 1791 kW Liquid specific power 619 kWh/t

In this case, 10.7% of the product is produced as saturated liquid at1.1 bar. The total power including product recompression to 30 bar andnet of the power generation from the expander of 364 kW is 2570 kW. 69tonnes per day of liquid is produced. Compared to Example 2, the totalpower is 1791 kW higher for the production of 69 tonnes per day liquid,meaning that the specific power for the liquid production is 619 kWh/t.

Example 6

A computer simulation of the process depicted in FIG. 7 has been carriedout using Aspen Plus. The resultant heat and mass balance data for thekey streams is presented in Table 7.

TABLE 7 90 100 104 105 106 110 111 114 118 119 124 Temperature C. 48.9−144.7 −151.7 −191.4 −147.3 −154.9 −158.5 −189.3 47.0 Pressure bar 50.030.0 25.0 1.5 30.0 30.0 25.0 25.0 25.0 Molar Flow kmol/s 0.278 0.2750.269 0.025 0.275 0.275 0.033 0.006 0.006 Vapour Fraction 1.00 1.00 0.000.49 0.85 0.05 1.00 1.00 1.00 Mole fraction Nitrogen 0.9200 0.92830.9473 0.9473 0.9283 0.9283 0.8271 0.1000 0.1000 Mole fraction Methane0.0500 0.0504 0.0515 0.0515 0.0504 0.0504 0.0010 0.0000 0.0000 Molefraction Helium 0.0200 0.0202 0.0000 0.0000 0.0202 0.0202 0.1719 0.90000.9000 Mole fraction Ethane 0.0080 0.0011 0.0012 0.0012 0.0011 0.00110.0000 0.0000 0.0000 Mole fraction Propane 0.0020 0.0000 0.0000 0.00000.0000 0.0000 0.0000 0.0000 0.0000 126 128 134 138 142 144 146 164 168170 172 Temperature C. −157.0 47.0 −156.9 −109.5 −181.0 −157.0 47.0Pressure bar 1.5 1.5 19.2 19.2 1.5 1.5 1.5 Molar Flow kmol/s 0.025 0.0250.200 0.200 0.200 0.200 0.200 Vapour Fraction 1.00 1.00 0.13 1.00 1.001.00 1.00 Mole fraction Nitrogen 0.9473 0.9473 0.9473 0.9473 0.94730.9473 0.9473 Mole fraction Methane 0.0515 0.0515 0.0515 0.0515 0.05150.0515 0.0515 Mole fraction Helium 0.0000 0.0000 0.0000 0.0000 0.00000.0000 0.0000 Mole fraction Ethane 0.0012 0.0012 0.0012 0.0012 0.00120.0012 0.0012 Mole fraction Propane 0.0000 0.0000 0.0000 0.0000 0.00000.0000 0.0000 180 181 186 188 190 191 193 194 196 199 Temperature C.−151.7 −187.3 −194.6 −194.6 47.0 −37.7 −65.7 −142.9 −150.7 18.5 Pressurebar 25.0 25.0 1.1 1.1 1.1 50.0 30.0 30.0 50.0 30.0 Molar Flow kmol/s0.044 0.044 0.040 0.004 0.004 0.262 0.262 0.262 0.015 0.002 VapourFraction 0.00 0.00 0.00 1.00 1.00 1.00 1.00 0.99 0.00 0.00 Mole fractionNitrogen 0.9473 0.9473 0.9428 0.9976 0.9976 0.9200 0.9200 0.9200 0.92000.0000 Mole fraction Methane 0.0515 0.0515 0.0559 0.0024 0.0024 0.05000.0500 0.0500 0.0500 0.0100 Mole fraction Helium 0.0000 0.0000 0.00000.0000 0.0000 0.0200 0.0200 0.0200 0.0200 0.0000 Mole fraction Ethane0.0012 0.0012 0.0013 0.0000 0.0000 0.0080 0.0080 0.0080 0.0080 0.7685Mole fraction Propane 0.0000 0.0000 0.0000 0.0000 0.0000 0.0020 0.00200.0020 0.0020 0.2215 Product recompression 3411 kW Expander power −363kW Warm expander power −183 kW Total 2864 kW Liquid production (1.1bara) 94 TPD Power with no liquid (Example 4) 757 kW Additional powerfor Liquid 2107 kW Liquid specific power 537 kWh/T

In this case, the feed is at 50 bar as in Example 3, but is expanded inwarm expander 192 prior to separation in NGL recovery column 96. A smallpart of the high pressure feed is condensed and fed to the top of theNGL recovery column as reflux. This column is reboiled with an externalheat source such as steam, hot oil or cooling water. The liquidproduction is higher than in Example 5 because of the higher feedpressure and additional refrigeration provided by the warm expander. Thespecific power for liquid production is also lower as the warm and coldexpander system provides refrigeration more efficiently than a singleexpander. The total power including product recompression to 50 bar andnet of the power generation from the expanders of 546 kW is 2864 kW. 94tonnes per day of liquid is produced. Compared to Example 3 (which alsohas a feed pressure of 50 bar), the total power is 2107 kW higher forthe production of 94 tonnes per day liquid, meaning that the specificpower for the liquid production is 537 kWh/t.

Example 7

A computer simulation of the process depicted in FIG. 8 has been carriedout using Aspen Plus. The resultant heat and mass balance data for thekey streams is presented in Table 8.

TABLE 8 90 100 104 105 106 110 111 114 118 119 124 Temperature C. 48.9−144.6 −151.8 −147.5 −155.7 −159.0 −189.3 46.9 Pressure bar 30.0 30.025.0 30.0 30.0 25.0 25.0 25.0 Molar Flow kmol/s 0.278 0.278 0.272 0.2780.278 0.030 0.006 0.006 Vapour Fraction 1.00 1.00 0.00 0.85 0.04 1.001.00 1.00 Mole fraction Nitrogen 0.9300 0.9300 0.9489 0.9300 0.93000.8090 0.1000 0.1000 Mole fraction Methane 0.0500 0.0500 0.0511 0.05000.0500 0.0009 0.0000 0.0000 Mole fraction Helium 0.0200 0.0200 0.00000.0200 0.0200 0.1902 0.9000 0.9000 126 128 134 138 142 144 146 164 168170 172 Temperature C. −151.8 −116.3 −183.7 −155.6 46.9 Pressure bar25.0 18.2 1.5 1.5 1.5 Molar Flow kmol/s 0.239 0.208 0.208 0.227 0.227Vapour Fraction 0.00 1.00 0.99 1.00 1.00 Mole fraction Nitrogen 0.94890.9413 0.9413 0.9947 0.9947 Mole fraction Methane 0.0511 0.0587 0.05870.0053 0.0053 Mole fraction Helium 0.0000 0.0000 0.0000 0.0000 0.0000180 181 186 188 190 191 193 194 196 199 200 Temperature C. −153.2 −188.2−195.1 −195.1 46.9 −151.6 Pressure bar 25.0 25.0 1.1 1.1 1.1 25.0 MolarFlow kmol/s 0.031 0.031 0.029 0.002 0.002 0.239 Vapour Fraction 0.000.00 0.00 1.00 1.00 0.22 Mole fraction Nitrogen 0.9990 0.9990 0.99890.9999 0.9999 0.9489 Mole fraction Methane 0.0010 0.0010 0.0011 0.00000.0000 0.0511 Mole fraction Helium 0.0000 0.0000 0.0000 0.0001 0.00010.0000 210 222 226 250 252 270 274 276 Temperature C. −151.6 −150.3−191.3 −151.8 −188.5 −167.1 −166.3 46.9 Pressure bar 25.0 18.2 1.5 25.025.0 1.5 6.0 6.0 Molar Flow kmol/s 0.208 0.208 0.227 0.033 0.033 0.0130.013 0.013 Vapour Fraction 0.00 1.00 1.00 0.00 0.00 0.00 0.00 1.00 Molefraction Nitrogen 0.9413 0.9413 0.9947 0.9489 0.9489 0.0500 0.05000.0500 Mole fraction Methane 0.0587 0.0587 0.0053 0.0511 0.0511 0.95000.9500 0.9500 Mole fraction Helium 0.0000 0.0000 0.0000 0.0000 0.00000.0000 0.0000 0.0000 Product recompression 2868 kW Expander power −354kW Pump power 1 kW Total 2515 kW Liquid production (1.1 bara) 70 TPDPower with no liquid (Example 3) 779 kW Additional power for Liquid 1736kW Liquid specific power 596 kWh/T

In this case, the total power including product recompression to 30 barand net of the power generation from the expander of 354 kW is 2515 kW.70 tonnes per day of liquid is produced. Compared to Example 2, thetotal power is 1736 kW higher for the production of 70 tonnes per dayliquid, meaning that the specific power for the liquid production is 596kWh/t.

Example 8

A computer simulation of the process depicted in FIG. 9 has been carriedout using Aspen Plus. The resultant heat and mass balance data for thekey streams is presented in Table 9.

TABLE 9 90 100 104 105 106 110 111 114 118 119 124 Temperature C. 48.9−145.4 −151.8 −155.6 −159.9 −189.3 46.9 Pressure bar 50.0 30.0 25.0 30.025.0 25.0 25.0 Molar Flow kmol/s 0.278 0.275 0.270 0.275 0.032 0.0080.008 Vapour Fraction 1.00 1.00 0.00 0.04 1.00 1.00 1.00 Mole fractionNitrogen 0.9200 0.9286 0.9477 0.9286 0.7784 0.1000 0.1000 Mole fractionMethane 0.0500 0.0504 0.0514 0.0504 0.0008 0.0000 0.0000 Mole fractionHelium 0.0200 0.0202 0.0000 0.0202 0.2208 0.9000 0.9000 Mole fractionEthane 0.0080 0.0008 0.0008 0.0008 0.0000 0.0000 0.0000 Mole fractionPropane 0.0020 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 126 128 134 138142 144 146 164 168 170 172 Temperature C. −123.0 −184.9 46.9 Pressurebar 18.2 1.5 1.5 Molar Flow kmol/s 0.227 0.227 0.243 Vapour Fraction1.00 0.98 1.00 Mole fraction Nitrogen 0.9442 0.9442 0.9947 Mole fractionMethane 0.0549 0.0549 0.0053 Mole fraction Helium 0.0000 0.0000 0.0000Mole fraction Ethane 0.0009 0.0009 0.0000 Mole fraction Propane 0.00000.0000 0.0000 180 181 186 188 190 191 193 194 196 199 200 Temperature C.−189.2 −195.1 −195.1 46.9 −38.6 −66.6 −143.6 −160.0 18.2 −151.4 Pressurebar 25.0 1.1 1.1 1.1 50.0 30.0 30.0 50.0 30.0 25.0 Molar Flow kmol/0.044 0.041 0.003 0.003 0.264 0.264 0.264 0.014 0.003 0.241 s VapourFraction 0.00 0.00 1.00 1.00 1.00 1.00 0.98 0.00 0.00 0.30 Mole fractionNitrogen 0.9990 0.9989 0.9999 0.9999 0.9200 0.9200 0.9200 0.9200 0.00000.9477 Mole fraction Methane 0.0010 0.0011 0.0000 0.0000 0.0500 0.05000.0500 0.0500 0.0100 0.0514 Mole fraction Helium 0.0000 0.0000 0.00010.0001 0.0200 0.0200 0.0200 0.0200 0.0000 0.0000 Mole fraction Ethane0.0000 0.0000 0.0000 0.0000 0.0080 0.0080 0.0080 0.0080 0.7759 0.0008Mole fraction Propane 0.0000 0.0000 0.0000 0.0000 0.0020 0.0020 0.00200.0020 0.2141 0.0000 210 222 226 250 252 270 274 276 280 288 302Temperature C. −151.4 −191.3 −189.0 −164.1 −163.2 46.9 46.9 40.0 46.9Pressure bar 25.0 1.5 25.0 1.5 6.0 6.0 1.5 18.2 25.0 Molar Flow kmol/s0.196 0.243 0.029 0.013 0.013 0.013 0.031 0.031 0.006 Vapour Fraction0.00 1.00 0.00 0.00 0.00 1.00 1.00 1.00 1.00 Mole fraction Nitrogen0.9362 0.9947 0.9477 0.0330 0.0330 0.0330 0.9947 0.9947 0.0000 Molefraction Methane 0.0628 0.0053 0.0514 0.9500 0.9500 0.9500 0.0053 0.00530.0000 Mole fraction Helium 0.0000 0.0000 0.0000 0.0000 0.0000 0.00000.0000 0.0000 1.0000 Mole fraction Ethane 0.0010 0.0000 0.0008 0.01670.0167 0.0167 0.0000 0.0000 0.0000 Mole fraction Propane 0.0000 0.00000.0000 0.0003 0.0003 0.0003 0.0000 0.0000 0.0000 304 312 314 TemperatureC. 46.9 40.0 −150.0 Pressure bar 1.3 25.0 25.0 Molar Flow kmol/s 0.0020.002 0.002 Vapour Fraction 1.00 1.00 1.00 Mole fraction Nitrogen 0.35710.3571 0.3571 Mole fraction Methane 0.0000 0.0000 0.0000 Mole fractionHelium 0.6429 0.6429 0.6429 Mole fraction Ethane 0.0000 0.0000 0.0000Mole fraction Propane 0.0000 0.0000 0.0000 Product recompression 3741 kWExpander power −369 kW Warm expander power −183 kW Tail gas compression29 kW Recycle compression 332 kW Pump power 1 kW Total 3550 kW Liquidproduction (1.1 bara) 100 TPD Power with no liquid (Example 4) 757 kWAdditional power for Liquid 2793 kW Liquid specific power 670 kWh/T

The total power including recycle and tail gas compression as well asproduct recompression to 50 bar and net of the power generation from theexpanders of 552 kW is 3550 kW. 100 tonnes per day of liquid isproduced. Compared to Example 3 (which also has a feed pressure of 50bar), the total power is 2793 kW higher for the production of 100 tonnesper day liquid, meaning that the specific power for the liquidproduction is 670 kWh/t.

While the invention has been described with reference to the preferredembodiments depicted in the figures, it will be appreciated that variousmodifications are possible within the spirit or scope of the invention.

In this specification, unless expressly otherwise indicated, the word‘or’ is used in the sense of an operator that returns a true value wheneither or both of the stated conditions are met, as opposed to theoperator ‘exclusive or’ which requires only that one of the conditionsis met. The word ‘comprising’ is used in the sense of ‘including’ ratherthan to mean ‘consisting of’. All prior teachings above are herebyincorporated herein by reference. No acknowledgement of any priorpublished document herein should be taken to be an admission orrepresentation that the teaching thereof was common general knowledge inAustralia or elsewhere at the date thereof.

1. Apparatus for recovering helium from a nitrogen-rich feed gascomprising helium, said apparatus comprising: a distillation columnsystem for operation at an elevated operating pressure to separate atleast partially condensed feed gas into helium-enriched overhead vaporand nitrogen-enriched bottoms liquid(s); an overhead condenser forpartially condensing helium-enriched overhead vapor by indirect heatexchange to produce helium-enriched vapor as product and liquid forreflux in the column system; a first heat exchange system for coolingfeed gas by indirect heat exchange with a first nitrogen-enrichedbottoms liquid to produce cooled feed gas and vapor for the columnsystem; a first pressure reduction device for reducing the pressure of asecond nitrogen-enriched bottoms liquid to produce reduced pressurebottoms liquid; a second heat exchange system for cooling said cooledfeed gas by indirect heat exchange against said reduced pressure bottomsliquid to produce at least partially condensed feed gas and vaporizedbottoms liquid; and a second pressure reduction device for reducing thepressure of said at least partially condensed feed gas to produce atleast partially condensed feed gas at reduced pressure for use as saidfeed to the distillation column system.
 2. The apparatus of claim 1comprising a third pressure reduction device for reducing the pressureof a third nitrogen-enriched bottoms liquid to produce reduced pressurebottoms liquid for vaporization by indirect heat exchange in saidoverhead condenser to produce nitrogen-enriched vapor.
 3. The apparatusof claim 2 comprising an expander for expanding said nitrogen-enrichedvapor to produce expanded nitrogen-enriched vapor for warming byindirect heat exchange in said overhead condenser to produce warmednitrogen-enriched vapor.
 4. The apparatus of claim 2 comprising a fourthpressure reduction device for reducing the pressure of a fourthnitrogen-enriched bottoms liquid to produce reduced pressure bottomsliquid for vaporization by indirect heat exchange in said overheadcondenser to produce nitrogen-enriched vapor.
 5. The apparatus of claim1 comprising an expander for expanding said vaporized bottoms liquid toproduce expanded nitrogen-enriched vapor for warming by indirect heatexchange in said overhead condenser to produce warmed nitrogen-enrichedvapor.
 6. The apparatus of claim 5 comprising: a fourth pressurereduction device for reducing the pressure of a fourth portion of saidnitrogen-enriched bottoms liquid to produce reduced pressure bottomsliquid; and a storage vessel for storing said reduced pressure bottomsliquid.
 7. Apparatus substantially as hereinbefore described withreference to the accompanying examples and/or drawings.